The words which, wich, witch sound the same but have different meanings and spellings. Why do which, wich, witch sound the same even though they are completely different words?
The answer is simple: which, wich, witch are homophones of the English language.
What particular one or ones: Which of these is yours?
The one or ones previously mentioned or implied, specifically:
Used as a relative pronoun in a clause that provides additional information about the antecedent: my house, which is small and old.
What particular one or ones: Which of these is yours?
A bundle of thread. Alternative spelling of wick.
A hag.
A woman claiming or popularly believed to possess magical powers and practice sorcery.
A believer or follower of Wicca; a Wiccan.
A woman considered to be spiteful or overbearing.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").